Abstract
Objectives : Spinal cord ischemia during surgical interventions sometimes results in paraplegia or paraparesis. Using dogs, we investigated whether spinal cord monitoring can be a useful method of detecting spinal cord ischemia.
Materials and methods : Thirty young mongrel dogs were used. The thoracic cavity was opened and the aorta was exposed and clamped above the T6 vertebral body for two hours (Experiment 1) or one hour (Experiment 2). In Experiment 2, the animals were maintained for 24 hours postoperatively to check for the presence of paralysis. Transcranial electrical stimulation was given according to Levy's method and descending motor evoked potentials (MEP) were recorded with an 8-channel mapping electrode placed on the posterior portion of the dura at the T10 level after laminectomy. Spinal cord blood flow (SCBF) was also measured with a Laser-Doppler flow meter, placing the probe directly on the dorsal surface of the spinal cord at the level of T11. The spinal cords from 15 dogs in Experiment 2 were examined histologically.
Results : In Experiment 1, the MEP amplitudes were at least 50% or more of the preclamping level in 10 dogs, but lower amplitudes were noted in five dogs.
SCBF was maintained between 25 and 75% of the pre-clamping value in the former, whereas it was 20% or less in the latter. In Experiment 2, 11 dogs maintained 50% or more of the MEP amplitude and 25% or more of the blood flow. These animals showed no sign of spinal cord damage, but histology of the spinal cord demonstrated slight evidence of hemorrhage and congestion. Four dogs showed below 50% amplitude and below 20% SCBF. Two of these animals showed complete paralysis of the hind limbs, whereas the remaining two did not show paralysis. In the two paralysed dogs, there was evidence of necrosis in the posterior horn and sporadic necrosis in the anterior horn. In the remaining two dogs, however, slight necrosis was found in the posterior horn.
Conclusion : MEP definitely detected spinal cord ischemia in the present animal model. When the MEP amplitude rapidly decreased to 50% or less of the pre-clamping level, there was a definite possibility of irreversible changes in the spinal cord. This method could be a useful adjunct to spinal cord monitoring.